1. Field of the Invention
This invention relates to a scroll-type fluid machine that functions as a compressor, and more particularly to an oilless scroll-type fluid machine wherein a chip seal is fitted into a seal groove that is rectangular in cross-section and formed in a helical wrap end surface which is opposed to a slide surface of an associated scroll so that the surrounded space between said slide surface and the wrap is sealed with the chip seal.
2. Description of the Prior Art
Scroll-type compressors which are known in the art include a stationary scroll having a first wrap formed in an involute spiral located within a casing enclosed by circumferential walls, a suction port and a discharge port formed in the circumferential wall and in the central region respectively, and an orbiting scroll having a second wrap formed in an involute spiral capable of mating with the first wrap, wherein the orbiting scroll is orbited without spinning to introduce a gas into the casing from the suction port and to take the gas into a closed space formed between the first wrap and the second wrap, as the orbiting scroll is orbited. The volume of the gas is gradually reduced with the gas being moved toward the center, and the thus compressed high-pressure air can be discharged outside from the discharge port.
The above scroll-type fluid machine can be a single unit scroll-type machine for expanding, compressing, or pumping fluid with a stationery scroll and an orbiting scroll interfitting each other, as disclosed, for example, in U.S. Pat. No. 4,192,152 and a twin unit scroll-type machine for expanding, compressing, or pumping fluid utilizing a pair of stationary scrolls having respectively a wrap inside and an orbiting scroll having a wrap on both surfaces which are interfitted with the stationary scrolls as suggested in Japanese Patent Publication 63-42081.
However, in either of the above scroll-type fluid machines, since the wraps of the scrolls have approximately the same number of turns and are mated with each other with the phase displaced 180 degrees, problems described below arise at the suction side as well as the discharge side.
That is, on the suction side, the wrap starting ends situated on the scroll outer circumferential side come in contact with the other wrap side wall surface at the position where the phases are displaced 180 degrees to form a compression chamber, and therefore it is necessary that a suction port is formed at each wrap starting end position, or a semicircular detour in communication with the suction port positioned 180 degrees away is formed on the wrap outer circumferential side, resulting in that the apparatus is made large and the number of steps of producing it increases.
The arrangement of a number of suction ports as described above means that a number of compression chambers with the phases displaced 180 degrees carry out simultaneously the compression step, which makes difficult the high compression, and small the volume of the gas to be taken into the closed space enclosed by the wraps, so that the suction efficiency is not improved.
On the other hand, on the discharge side, since it is necessary to arrange a bearing section where a main shaft (crank shaft) is inserted so as to orbit the orbiting scroll at the central part of the scroll, a wrap terminal end and a discharge port must be disposed on the bearing section outer circumferential side in the involute spiral, and the arrangement of the wrap starting ends with the phases displaced 180 degrees makes short the involute spiral that can form a closed space (compression chamber), which results in that the volume of the final compression chamber remains large to be opened to the discharge port and therefore the compression ratio becomes small.
The large volume of the final compression chamber makes the seal line longer and as a result the sealability lowers and leakage is liable to occur, thereby lowering the compression efficiency.
To solve the above problems, in the so-called single unit scroll-type fluid machine, a main shaft of the orbiting scroll is disposed on the wrap back side so that a discharge port is arranged at the stationary scroll central section, while in the twin unit scroll-type fluid machine, as shown in the embodiment below, since an orbiting scroll is disposed between a pair of stationary scrolls, a main shaft must be extended through the stationary scroll central section, and therefore a defect inevitably arises that a wrap terminal end and a discharge port have to be disposed on the bearing section outer circumferential side in the middle of the involute spiral in the fluid machine adopting the above constitution.
Particularly in a compressor out of these fluid machines, in order to obtain a clean compressed gas, a groove section is formed in a wrap end surface opposed to the associated scroll specular surface and a self-lubricating seal member (hereinafter referred to as chip seal) is fitted into said groove section, thereby an oilless compressor is suggested wherein the wrap end surface is allowed to come slidably in contact with the associated scroll not directly but through said chip seal so that oilless sealing becomes possible without using an oil seal (see, for example, German Patent DE No. 3,538,522).
However, in a twin unit scroll-type fluid machine, since a bearing section wherein a rotating shaft and others are inserted is situated at the scroll central section, a wrap terminal end and a discharge port are required to be disposed halfway of the helical curve on the bearing section outer circumferential side and in this state the wraps of the scrolls are mated with each other with the numbers of the turns being the same and with the phases being displaced 180 degrees.
Therefore, the gas is released to the discharge port while the volume of the final compressed chamber remains large on the discharge side, so that the compression ratio becomes small.
Further, since the large volume of the final compression chamber makes the seal line longer, the sealability lowers and a backward flow is liable to occur, leading to lowering of the compression efficiency.
In the scroll-type fluid machine using the chip seal, as shown in the above-mentioned German Patent and EPC patent No. 029,8315, a resilient backup member is disposed in the interior of the groove section on the chip seal back side and a floating effect is increased through the backup member to increase the sealing effect.
However, the chip seal groove is not easily made deeper, since the machining tools have a limit and the number of steps of cutting required for making the groove deeper increases.
Further, if the groove is too deep, when the wraps are orbited, a force is exerted transversely of the chip by the sliding engagement with the scroll specular surface, and a collapse will occur, which is unfavorable in view of the strength. If the width of the wrap is increased to solve this problem, the width of the wrap does not contribute to the compression efficiency at all, and problems arise in that a dead space increases and the compression efficiency and the amount of the air decrease.
Therefore, a backup member is disposed in the interior of the groove section on the chip seal back side without making the groove of the chip seal deep and the chip seal upper section is extended out of the groove section. However in that configuration, the amount of the chip seal in the groove decreases and the chip seal is subjected to an energized force due to the small spring constant of the backup member, resulting in a problem in that the assembly of the chip seal becomes impossible because the chip seal attached in an involute fashion is disengaged from the seal groove unless the assembly is carried out very carefully.